Organosiloxanes comprising amino groups, referred to as aminosilanes in short, are used as adhesion agents, as crosslinking agents for curable materials as well as building components of silane functional polymers, among other uses. Owing to the ease of their manufacture, aminosilanes having primary amino groups (“primary aminosilanes”) are very common; however, they can have several drawbacks when used. Owing to the relatively hydrophilic primary group, they can have undesired moisture absorbing properties, which can have a negative effect on the adhesion of a cured composition, which is exposed to moisture, to the substrate. In the use of silane functional polymers as building components, polymers which are prepared by the addition reaction of isocyanate functional polyurethane polymers to aminosilanes, primary aminosilanes can lead to high viscosities, can make it difficult to process the silane functional polymers, and can worsen the application properties as well as the ductility of the products prepared therefrom. Therefore, it can be advantageous to use, instead of the primary aminosilanes, those that have secondary amino groups (“secondary aminosilanes”); they are hydrophobic and they lead to low viscosity, silane functional polyurethane polymers. However, the availability of cost effective and stockable secondary amines is limited. The silane crosslinking polyurethanes produced from the secondary aminosilanes that are known can take a long time to cure, and can often have a low resistance to heating.
It is known to prepare secondary aminosilanes by hydrosilylation of allylsilanes, as described in U.S. Pat. No. 6,197,912, for example, or by nucleophilic substitution of chloro- or bromoalkylsilanes with primary amines, or of alkyl- or aryl halides with primary aminosilanes, as described in U.S. Pat. No. 3,676,478 or U.S. Pat. No. 6,197,912, for example. Due to the expensive manufacture and the much smaller quantities in comparison to the primary aminosilanes, they are considerably more expensive than the primary aminosilanes.
Therefore, for the manufacturers of silane functional polymers, it can be more advantageous to produce secondary aminosilanes starting from primary aminosilanes. The addition reaction with Michael acceptors, for example, acrylonitrile, acrylic acid ester, and maleic acid ester, is known, and has been described in U.S. Pat. No. 3,033,815, U.S. Pat. No. 4,067,844 and U.S. Pat. No. 5,364,955, for example. These reagents are inexpensive, and the reaction to form the secondary aminosilane succeeds already under mild conditions. However, it can be slow and incomplete, thus leaving a portion of the Michael acceptors in an unadducted form, which may involve their subsequent removal, if one wishes to prevent interfering odors of the products produced with the addition products. The Michael adducts of primary aminosilanes can include additional functional groups, such as cyano groups, and for example ester groups. The presence of ester groups leads to silane functional polyurethane polymers having a relatively low viscosity. However, this is associated with an issue whereby the ester groups are capable of reacting with primary or secondary amino groups, and in the process they form amides. In silane crosslinking curable materials, which can be formulated with primary amines and aminosilanes as catalysts and adhesives, this can be undesirable, because it can lead to the deactivation of the amines and to an increased crosslinking density and thus to increased brittleness of the cured polymer. Due to the creeping self condensation to form polyamides, incompletely alkylated aminosilanes with ester groups are also often unsuitable for storage.